Deep Brain Stimulation (DBS) has been found to be successful in treating a variety of brain-controlled disorders, including movement disorders. Generally, such treatment involves placement of a DBS type lead through a burr hole drilled in the patient's skull, followed by placement of the lead and then applying appropriate stimulation through the lead to the physiological target. The placement portion of the treatment is very critical, and has been the subject of much attention and research. In particular, finding the deep brain target and then placing the permanent lead so that it efficiently stimulates such target is very important. See, for example, U.S. patent application Ser. No. 09/009,247, filed Jan. 20, 1998, now U.S. Pat. No. 6,011,996, Gielen et al, which deals with the localization procedure in functional stereotactic brain surgery, i.e., the initial probing to find the optimum site for delivering the stimulation.
Finding the optimal physiological target in deep brain stimulation implants for the treatment of movement disorders is a particularly complicated task. This is especially true for the treatment of symptoms which cannot be tested at the operating table during lead implant. For instance, it is impossible to test walking and postural stability in Parkinson's Disease (PD) patients during DSB lead implant. Two other major PD symptoms, Rigidity and Akinesia, are also considered difficult to evaluate quantitatively during DBS lead implant. Thus far, no reliable quantitative evaluation procedures exist that can be performed during the surgical DBS implant procedure for these major symptoms.
A recent procedure has been suggested which allows post-operative quantitative testing of muscle function in PD. See Pascual-Leone, Rapid Rate Transcranial Magnetic Stimulation (rTMS) in Movement Disorders; Movement Disorders, Vol 11, Suppl. #1, pp.:23, 1966. In this procedure, trans-cranial magnetic stimulation of the motor cortex is used to show that the brain is able to control muscle movements in a normal way when and if the DBS electrode is implanted in the optimal physiological position in the Globus Pallidum Internae (GPi) and electrical stimulation with the appropriate parameters is applied through the DBS electrode. Thus, it was shown that those areas of the motor cortex (MC) which are involved in the control of movement in the muscle of the thumb can only be activated if the appropriate DBS stimulation is concurrently applied to the correct part of the GPi.
Based on this finding, it is reasonable that an improved procedure could be utilized for optimizing the implant position of the DBS electrode(s) in the GPi or other neuro-modulation target for treating disorders, and particularly movement disorders, by means of deep brain stimulation. Thus, if postural instability of the patient is a major PD symptom, one might be able to find the optimal physiological target for the DBS electrode by seeing when trans-cranial magnetic stimulation of the motor cortex achieves optimal control movement of the leg muscles. However, this magnetic stimulation procedure is not suitable for intra-operative use, i.e., for testing lead position while the lead is stereotactically held. The applied very fast changing and very strong magnetic fields may interact with the DBS electrode in a comparable way as suggested for MRI imaging procedures, which is contra-indicated for DBS patients. Further, the trans-cranial magnetic stimulation coil cannot be accessed to the relevant sites of the brain when the DBS lead is being held by the stereotactic equipment. This means that the Leone procedure is not directly suggested for use in evaluating the excitability of the relevant motor cortex areas during lead implant. Thus, while the prior art procedure is appropriate for certain post-surgical testing because it is non-invasive, it is not suggested for intra-operative use.
The continued need in the art is a system and procedure that can be utilized during surgery when the DBS lead is being implanted, to determine when it has been placed in the optimal position for stimulation therapy of the patient's particular disorder, or for recording of brain activity. In general terms, the aim is a system and method for stimulation of the GPi or other neuro-stimulation target, and a feedback target such as the MC. A key to this invention is the recognition that during surgery, there is no need for a non-invasive way of stimulating the feedback target. The invention, rather, provides apparatus and a method of testing for the optimal DBS electrode position during the invasive surgery, and as part of the localization test procedure that is required in any event, enabling a reliable determination of optimal lead placement before permanent lead implant and close of surgery.